Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, world demand for phenol is growing more rapidly than that for acetone. In addition, the cost of propylene is likely to increase, due to a developing shortage of propylene. Thus, a process that uses higher alkenes instead of propylene as feed and coproduces higher ketones, rather than acetone, may be an attractive alternative route to the production of phenols.
For example, oxidation of cyclohexylbenzene (analogous to cumene oxidation) could offer an alternative route for phenol production without the problem of acetone co-production. This alternative route co-produces cyclohexanone, which has a growing market and is used as an industrial solvent, as an activator in oxidation reactions and in the production of adipic acid, cyclohexanone resins, cyclohexanone oxime, caprolactam and nylon 6. Moreover, cyclohexanone and phenol are readily interconverted by dehydrogenation and hydrogenation, respectively, so that the cyclohexylbenzene route offers the potential not only for producing a mixture of phenol and cyclohexanone but also for maximizing the production of phenol or cyclohexanone according to market demand.
It is well known cyclohexylbenzene can be produced from benzene by the process of hydroalkylation or reductive alkylation. In this process, benzene is heated with hydrogen in the presence of a catalyst such that the benzene undergoes partial hydrogenation to produce cyclohexene which then alkylates the benzene starting material. An example of such a process is described in U.S. Pat. No. 6,037,513.
However, despite its potential advantages, no commercial process for manufacture of phenol and/or cyclohexanone via the hydroalkylation of benzene and the oxidation and cleavage of the resultant cyclohexylbenzene, has yet been developed. Among the problems that need to be addressed in a commercial process are the relatively low conversion rate in the hydroalkylation step and the tendency for the hydroalkylation to generate significant quantities of by-products, such as cyclohexane. The present invention seeks to provide an efficient and economical cyclohexylbenzene-based process for the production of phenol and/or cyclohexanone from benzene, in which the problems inherent in the commercial application of the process are alleviated.